We propose to survey all sources of skin cancer care (i.e. dermatology practices, dermatopathologists, plastic surgeons, radiation therapy units, pathology laboratories) to determine the incidence of basal cell (BCC) and squamous cell (SCC) skin cancers in New Hampshire for the period July 1, 1993 to June 30, 1996. We will compare these incidence rates with those determined from a similar survey conducted in New Hampshire during 1979-80. We propose also to conduct a population-based case-control study involving the 300 eligible cases of SCC identified in the survey, a randomly drawn sample of 600 of the eligible BCC cases, and a population sample of 600 controls (selected by random digit dialing for those under age 65 yrs and by random selection from Medicare enrollees for those 65 yrs and older). Using a standardized questionnaire, we will conduct an in-person interview covering sun exposure history, sun sensitivity, cigarette smoking and medical exposures (e.g. radiation therapy). Cases and controls will also provide toenail clippings for determination of arsenic and selenium content using neutron activation analysis. A blood sample will be drawn to establish a white blood cell DNA bank for future studies of DNA repair genes and perhaps other genetic factors. This study will elucidate possible increases in non-melanoma skin cancer incidence over a 15-year period in a defined northern population, and it will clarify the contribution of sunlight exposure, skin sensitivity, environmental arsenic exposure, and other potential risk factors in determining BCC and SCC occurrence.